/*
 * Copyright (C) 2015 Apple Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
 */

#pragma once

#include "JSCell.h"
#include "include/JavaScriptCore/bytecode/Watchpoint.h"
#include "WriteBarrier.h"

namespace JSC {

// Allocate one of these if you'd like to infer a constant value. Writes to the value should use
// notifyWrite(). So long as exactly one value had ever been written and invalidate() has never been
// called, and you register a watchpoint, you can rely on the inferredValue() being the one true
// value.
//
// Commonly used for inferring singletons - in that case each allocation does notifyWrite(). But you
// can use it for other things as well.

    class InferredValue : public JSCell {
    public:
        typedef JSCell Base;

        static InferredValue *create(VM &);

        static const bool needsDestruction = true;

        static void destroy(JSCell *);

        static Structure *createStructure(VM &, JSGlobalObject *, JSValue prototype);

        static void visitChildren(JSCell *, SlotVisitor &);

    DECLARE_INFO;

        // For the purpose of deciding whether or not to watch this variable, you only need
        // to inspect inferredValue(). If this returns something other than the empty
        // value, then it means that at all future safepoints, this watchpoint set will be
        // in one of these states:
        //
        //    IsWatched: in this case, the variable's value must still be the
        //        inferredValue.
        //
        //    IsInvalidated: in this case the variable's value may be anything but you'll
        //        either notice that it's invalidated and not install the watchpoint, or
        //        you will have been notified that the watchpoint was fired.
        JSValue inferredValue() { return m_value.get(); }

        // Forwards some WatchpointSet methods.
        WatchpointState state() const { return m_set.state(); }

        bool isStillValid() const { return m_set.isStillValid(); }

        bool hasBeenInvalidated() const { return m_set.hasBeenInvalidated(); }

        void add(Watchpoint *watchpoint) { m_set.add(watchpoint); }

        void notifyWrite(VM &vm, JSValue value, const FireDetail &detail) {
            if (LIKELY(m_set.stateOnJSThread() == IsInvalidated))
                return;
            notifyWriteSlow(vm, value, detail);
        }

        void notifyWrite(VM &vm, JSValue value, const char *reason) {
            if (LIKELY(m_set.stateOnJSThread() == IsInvalidated))
                return;
            notifyWriteSlow(vm, value, reason);
        }

        void invalidate(VM &vm, const FireDetail &detail) {
            m_value.clear();
            m_set.invalidate(vm, detail);
        }

        static const unsigned StructureFlags = StructureIsImmortal | Base::StructureFlags;

        // We could have used Weak<>. But we want arbitrary JSValues, not just cells. It's also somewhat
        // convenient to have eager notification of death.
        //
        // Also note that this should be a private class, but it isn't because Windows.
        class ValueCleanup : public UnconditionalFinalizer {
        WTF_MAKE_FAST_ALLOCATED;

        public:
            ValueCleanup(InferredValue *);

            virtual ~ValueCleanup();

        protected:
            void finalizeUnconditionally() override;

        private:
            InferredValue *m_owner;
        };

    private:
        InferredValue(VM &);

        ~InferredValue();

        JS_EXPORT_PRIVATE void notifyWriteSlow(VM &, JSValue, const FireDetail &);

        JS_EXPORT_PRIVATE void notifyWriteSlow(VM &, JSValue, const char *reason);

        friend class ValueCleanup;

        InlineWatchpointSet m_set;
        WriteBarrier<Unknown> m_value;
        std::unique_ptr<ValueCleanup> m_cleanup;
    };

// FIXME: We could have an InlineInferredValue, which only allocates the InferredValue object when
// a notifyWrite() transitions us towards watching, and then clears the reference (allowing the object
// to die) when we get invalidated.

} // namespace JSC
